1. Technical Field
The present invention relates to a piezoelectric oscillation circuit, a temperature-constant piezoelectric oscillator, and others.
2. Related Art
A temperature-constant piezoelectric oscillator increases frequency stability by using a constant-temperature oven for maintaining a constant operation temperature of an oscillator. For example, an oven controlled crystal oscillator (OCXO) which includes a crystal oscillator as a piezoelectric device produces frequency deviation of only about 0.05 ppm at the most, and thus has been employed in the field of radio-communication base station, wire network device, and others.
JP-A-2006-311496 discloses a temperature-constant piezoelectric oscillator which includes components such as a power transistor, a temperature-sensitive resistance (thermistor) and a chip resistance for heating. According to this structure, the operation temperature of the oscillator is kept constant by using the power transistor which supplies power controlled by the resistance of the thermistor to the chip resistance.
In this case, the temperature-constant piezoelectric oscillator thus constructed requires flow of a large current so as to maintain a predetermined operation temperature for the oscillator when used under a low-temperature environment. In an ideal condition, the ground resistance is small enough to be ignored, and the ground potential (GND) does not vary according to the use environment. In a practical situation, however, the ground resistance exhibits a small but definite value, and may produce deviation of some millivolts from the ground potential, for example, when a large current flows. When this change of the ground potential affects only one of the terminals of the oscillator, the direct current potential difference between the terminals of the oscillator varies and changes the oscillation frequency.